Caption: David Baltimore (b.1938), US molecular biologist and Nobel Laureate. Baltimore was educated in chemistry at Swarthmore and the Massachusetts Institute of Technology. In 1968 he showed how the polio virus replicates. In 1970 he announced the discovery of an enzyme called reverse transcriptase, which can transcribe RNA into DNA. This was found to occur in some tumour viruses. Reverse transcription went against the accepted 'central dogma', in which DNA transcribes to RNA. This work led to Baltimore receiving the 1975 Nobel Prize for Medicine or Physiology.